Imaginary Picture of KELT-21 b
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Exoplanet Name : KELT-21 b
Alternate Name :
Radius (Rjup / Re): 1.5860 (Rjup) 17.7775 (Rearth)
Mass (Mjup / Me): 3.9100 (Mjup) 1243.1376 (Mearth)
Semi Major Axis / Orbital Distance Calculated 0.0522 (AU) 0.0522 (AU Est.)
Eccentricity : 0.0000
Orbital Period(Yrs) 0.0099
Orbital Period(Observed/Estimated) 3.61 (Days Obs.) 3.61 (Days Est.)
Star Radiation at Atmospheric Boundary: 4018124.8 (W/m2)
Measured Temperature (K) 0.0 (K)
Blackbody T 0.1(K) 1998.2 (K)
Blackbody T 0.3(K) 1876.6 (K)
Blackbody T 0.7(K) 1518.3 (K)
Tidally Locked Blackbody T 0.1(K) 2376.3 (K)
Tidally Locked Blackbody T 0.3(K) 2231.6 (K)
Size Class: Super-Jupiter-size
Mass Class:
Detection Type : Primary Transit
Mass Detection : Radial Velocity
Radius Detection : Primary Transit
Habitability by Solar Eq. Astronomical Unit: Not habitable
Habitability by Kopparapu: Not habitable
Star Name : KELT-21
Alternate Name :
Star Distance(LY) : 1353.5
Stellar Radius(Rsun) : 1.6 (Rsun Measured)
Stellar Mass(Msun) : 1.5 (Msun Measured) 1.5 (Msun Estimated)
Star Age : 1.6 (GY)
Temperature : 7598 (K)
Spectral type : A8V
Metalicity : -0.4
Absolute Magnitude: 2.4
Apparent Magnitude: 10.5
Right Ascension(RA) 304.8000
Declination (DEC) 32.5811
Hubble Space Telescope Guide Star Catalog (GSC) ID
Discovered by
Discovery Paper - Authors
Discovery Paper - Title
Discovery Paper - Journal
Discovery Paper - URL
SIMBAD LINK
Open Exoplanet Database Link
KELT-21 b
KELT-21 b

  • KELT-21 b is an exoplanet orbiting the star KELT-21, located about 1353.5 light-years (415.0 pc) away from Solar System. Its discovery was publicly announced on 2017.
  • The host star KELT-21 has apparent magnitude of 10.5, with absolute magnitude of 2.4.
  • It is 1.5 times more massive and 1.6 times bigger compared with our Sun. The surface temperature is 7598 with its spectral types of A8V
  • In this planetary system, the extrasolar planet KELT-21 b orbits around the star KELT-21 every 3.6 days with its orbital distance of 0.05 AU ( 7814992.8 km)
  • (Projected orbit of KELT-21 b around its host star KELT-21)


  • The Star KELT-21 's habitable zone is located at the following distance
  • Inner Boundary (the orbital distance at Venus's Equivalent Radiation ) : 2.049 AU ( 306457735.6 km)
  • Earth Boundary (the orbital distance at Earth's Equivalent Radiation) : 2.832 AU ( 423604677.6 km)
  • Outer Boundary (the orbital distance at Mars's Equivalent Radiation) : 4.315 AU ( 645479785.2 km)
  • Snow Line (the orbital distance at Snow Line Equivalent Radiation) : 6.349 AU ( 949851780.6 km)
  • Radiation at Planetary Boundary of KELT-21 b : 4018124.84 W/m2

    (Habitable zone calculated based on SEAU(Solar Equivalent Astronomical Unit) around the star KELT-21)



  • Kopparapu Recent Venus for Star KELT-21 distance : 1.937 AU
  • Kopparapu Runaway Greenhouse for Earth-sized planet for Star KELT-21 distance : 2.453 AU
  • Kopparapu Runaway Greenhouse for Super-Earth-sized planet for Star KELT-21 distance : 2.369 AU
  • Kopparapu Runaway Greenhouse for Mars-sized planet for Star KELT-21 distance : 2.593 AU
  • Kopparapu Outer Boundary for Maximum Greenhouse for Star KELT-21 distance : 4.230 AU
  • Kopparapu Outer Boundary for Early Mars for Star KELT-21 distance : 4.460 AU

    (Habitable zone calculated based on Kopparapu et al.(2013) around the star KELT-21)



  • Original Kopparapu Recent Venus for Star KELT-21 distance : 2.009 AU
  • Original Kopparapu Runaway Greenhouse for Star KELT-21 distance : 2.507 AU
  • Original Kopparapu Moist Greenhouse for Star KELT-21 distance : 2.659 AU
  • Original Kopparapu Outer Boundary for Maximum Greenhouse for Star KELT-21 distance : 4.306 AU
  • Original Kopparapu Outer Boundary for Early Mars for Star KELT-21 distance : 4.478 AU

    (Habitable zone calculated based on Kopparapu et al.(Original) around the star KELT-21)



    (Position in Stellar Map of star KELT-21 and its Exoplanet KELT-21 b)



    (Zoomed position in Stellar Map of star KELT-21 and its Exoplanet KELT-21 b (zoom level 3))